Redundancy gateway system

ABSTRACT

A redundancy gateway system that can avoid short interruption of data communication caused by system switching in gateway units configured in a multiplex manner for a plurality of systems, and that can maintain the communication state prior to the system switching and avoid degradation of communication quality. A duplicate of a received packet is generated, thereby supplying the packet of the same content to a configuration of gateway units. For each packet, a common write pointer corresponding to identification information appended to the packet is generated. Each gateway unit writes the packet to its own jitter buffer in accordance with the common write pointer corresponding to each supplied packet, sequentially reads out the written packet from the jitter buffer, and generates a TDM signal. One of the gateway units is selectively switched and only the TDM signal generated by the one gateway unit is supplied to a TDM network.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a redundancy gateway system thatincludes plural gateway units configured in a multiplex manner forplural systems and that carries out data communications such as audiodata communications and video data communication between a packetnetwork and a TDM network such as a telephone network.

2. Description of the Related Art

Generally, a gateway unit that connects a packet network and a telephonenetwork with each other and relays audio data has a function of encodingan audio signal received from the telephone network by an encoder, thenpacketizing the audio data in accordance with RTP (Real-time TransportProtocol) and sending the packetized data to the packet network.Conversely, the gateway unit also has a function of decoding an audiopacket received from the packet network by a decoder and then sendingthe decoded audio data to the telephone network. To restrain theinfluence of failure in the gateway unit on user's communication, thegateway unit is often has a multiple redundant configuration of duplexor more. For example, in a duplex redundant configuration in which oneof two gateway units is set for an operation system and the other one isset for a standby system, if failure occurs in the operation system orif maintenance of the unit is necessary, system switching is carried outbetween the units in the operation system and the standby system. Amethod has been proposed to prevent interruption of communication inthis system switching.

In the method disclosed in Japanese Patent Kokai No. 2005-57461, whenswitching between the operation system and the standby system is carriedout, RTP/RTCP session information except for information related to thetime stamp and sequence number, and connectivity information aretransferred from the operation system to the standby system. Thus, thegateway unit switched to the operation system can start a decodingoperation using a parameter value set for an RTP packet sent from an IPterminal as an initial value, and the operation system and the standbysystem can be switched without interrupting the audio.

However, the conventional technique cannot achieve the elimination ofshort interruption of speaking. In the disclosed method, since the timestamp value and sequence number of the RTP session information to besent to the packet network are not taken over, occurrence of shortinterruption of speaking due to detection of discontinuity in the timestamp value and sequence number of the RTP packet in the receivingdevice cannot be avoided. Also, with respect to processing to performaudio processing of data received from the packet network and thenoutput the audio data to the telephone network, synchronization ofprocessing cannot be taken between the operation system and the standbysystem. Therefore, short interruption or duplication of speaking occursin system switching. Moreover, since the new operation system unitstarts operating with an initial state irrespective of the state of theformer operation system unit, degradation of the speaking quality cannotbe avoided until the new operation system restores a state equivalent tothe state of the former operation system. For example, speaking may beinterrupted while packets remaining in the jitter buffer of the formeroperation system are discarded, or a time of approximately 500 to 800 msmay be necessary in order to reach a state where echo can be properlyeliminated as optimization control is reset in the echo canceller of thenew operation system, and the speech during this period may not soundnormal.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a redundancy gateway systemthat can avoid, to the maximum extent, short interruption of datacommunication caused by system switching in gateway units configured ina multiplex manner for plural systems, and that can maintain thecommunication state prior to the system switching and avoid degradationof communication quality.

According to a first aspect of the invention, a redundancy gatewaysystem includes plural gateway units configured in a multiplex mannerbetween a packet network and a TDM network, and performs TDM conversionprocessing to plural packets supplied from the packet network, by thegateway units, and supplies a resulting TDM signal to the TDM network.The redundancy gateway system includes: a same packet supply unit thatgenerates a duplicate of the packet and thus supplies packets of thesame content to plural ones of the gateway units; a common write pointergenerating unit that generates, for each of the packets, a common writepointer corresponding to identification information appended to thepacket; and a selective supply unit that selectively switches one of theplural gateway units and supplies only a TDM signal acquired from theone gateway unit to the TDM network. Each of the plural gateway unitsincludes at least one jitter buffer, a unit that generates a readpointer for the jitter buffer, and a jitter buffer control unit thatwrites, for each supplied packet, the packet into the jitter buffer inaccordance with the common write pointer corresponding to the packet,and sequentially reads out a written packet from the jitter buffer inaccordance with the jitter buffer read pointer and provides it for theTDM conversion processing.

According to a second aspect of the invention, a redundancy gatewaysystem includes plural gateway units configured in a multiplex mannerbetween plural packet networks configured in a multiplex manner and aTDM network, and performs TDM conversion processing to plural packetssupplied from the packet networks, by the gateway units, and supplies aresulting TDM signal to the TDM network. The redundancy gateway systemincludes: a common write pointer generating unit that generates, foreach of the packets, a common write pointer corresponding toidentification information appended to the packet; and a selectivesupply unit that selectively switches one of the plural gateway unitsand supplies only a TDM signal acquired from the one gateway unit to theTDM network. Each of the plural gateway units includes at least onereceiving buffer, at least one jitter buffer, a unit that generates aread pointer for the jitter buffer, a same packet supply unit that takesin a packet supplied only from one of the packet networks, duplicatesthis packet to generate a packet of a same content, and supplies it toanother gateway unit different from a local gateway unit, a receivingbuffer control unit that sequentially writes and reads both a packettaken in by the local gateway unit and a packet supplied from anothergateway unit different from the local gateway unit into and from thereceiving buffer, a valid packet supply unit that uses a packet read outfirst from the receiving buffer as a valid packet and discards a packetof the same content read out in duplicate as an invalid packet, therebysupplying only the valid packet to the jitter buffer, and a jitterbuffer control unit that writes, for each packet supplied by the validpacket supply unit, the packet into the jitter buffer in accordance withthe common write pointer corresponding to the packet, and sequentiallyreads out a written packet from the jitter buffer in accordance with thejitter buffer read pointer and provides it for the TDM conversionprocessing.

According to the redundancy gateway system of the invention, shortinterruption of data communication caused by system switching betweengateway units configured in a multiplex manner for plural systems can beavoided to the maximum extent, and the communication state prior to thesystem switching can be maintained to avoid degradation of communicationquality.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an overall configuration including aredundancy gateway system according to an embodiment of the invention.

FIG. 2 is a chart showing an exemplary configuration of a TDM signal.

FIG. 3 is a chart showing input and output timing of audio data and apacket in two systems.

FIG. 4 is a flowchart showing an outline of an operation to packetize aTDM signal.

FIG. 5 is a chart showing an outline of a writing operation to a jitterbuffer in two systems.

FIG. 6 is a chart showing an outline of a reading operation from ajitter buffer in two systems.

FIG. 7 is a chart showing an operation in the case where a write pointerand a read pointer are not transferred between two systems.

FIG. 8 is a chart showing an operation in the case where a write pointerand a read pointer are transferred between two systems.

FIG. 9 is a block diagram showing a configuration of a network connectedto a redundancy gateway system according to a second embodiment.

FIG. 10 is a time chart showing a writing operation to a local-systemreceiving buffer and a remote-system receiving buffer.

FIG. 11 is a time chart showing a reading operation from a local-systemreceiving buffer and a remote-system receiving buffer of a presentgateway unit.

FIG. 12 is a time chart showing an operation in the case where awrite/read pointer for a receiving buffer is “not transferred” when aspare gateway unit is newly incorporated.

FIG. 13 is a time chart showing an operation in the case where awrite/read pointer for a receiving buffer is “transferred” when a sparegateway unit is newly incorporated.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention will be described in detail with referenceto the accompanying drawings. In the embodiments, the term “pointer”refers to an address defining the position where information is held.

First Embodiment

FIG. 1 shows an overall configuration including a redundancy gatewaysystem according to an embodiment of the invention. The redundancygateway system according to the invention is provided between a packetnetwork 70 and a telephone network 60, which is a TDM network. Theredundancy gateway system includes at least two gateway units 10 and 20configured in a multiplex manner to form plural systems, a control unit50, a TDM exchange unit 30, and two packet interface units 40 and 41.

The gateway unit 10 and the gateway unit 20 have the same internalconfiguration. The gateway unit 10 includes a packet selecting unit 100,an IP processing unit 101, an RTP/RTCP processing unit 102, a jitterbuffer control unit 103, a jitter buffer 104, an audio processing unit105, and a TDM processing unit 106. Similarly, the gateway unit 20includes a packet selecting unit 200, an IP processing unit 201, anRTP/RTCP processing unit 202, a jitter buffer control unit 203, a jitterbuffer 204, an audio processing unit 205, and a TDM processing unit 206.

Each of the packet selecting units 100 and 200 are connected to both thepacket network interface units 40 and 41 via a receiving packetconfounding line PL. The packet network interface units 40 and 41 have aphysical address and an IP address set in advance that are necessary forconnection with the packet network 70 by the control unit 50, and theyare connected to the packet network 70. Since the redundantconfiguration is provided, only the packet network interface unit of theoperation system, of the packet network interface units 40 and 41, isselectively switched to send and receive packets to and from the packetnetwork 70.

Also, the packet network interface units 40 and 41 have a function ofduplicating a received packet and output packets of the same content toboth the packet selecting unit 100 and the packet selecting unit 200connected thereto. The packet selecting units 100 and 200 select apacket from the packet network interface unit of the operation systemand output it to the IP processing unit 101 and the IP processing unit201.

Hereinafter, the internal connection in the two systems of the gatewayunits 10 and 20 will be described simultaneously. Therefore, in thefollowing description, it is assumed that component elements in onegateway unit are connected to other component elements in the samegateway unit in principle, unless there is a description that “acrossthe systems” or the like.

The IP processing unit 101 and the IP processing unit 201 are connectedto the RTP/RTCP processing unit 102 and the RTP/RTCP processing unit202, respectively. Of data in the RTP/RTCP processing unit 102 and theRTP/RTCP processing unit 202, data from the packet network 70, aresupplied to the jitter buffer 104 and the jitter buffer 204. Data fromthe telephone network 60 are supplied thereto via the audio processingunit 105 and the audio processing unit 205, respectively. Also, theRTP/RTCP processing unit 102 and the RTP/RTCP processing unit 202 areconnected to the jitter buffer control unit 103 and the jitter buffercontrol unit 203.

To synchronize the jitter buffer operation, the jitter buffer controlunit 103 and the jitter buffer control unit 203 are connected with eachother across the systems. A write pointer WP and a read pointer RP thatare commonly used in the redundancy gateway system according to theinvention can be supplied from one jitter buffer control unit to theother. Also, to synchronize the RTP/RTCP processing, the RTP/RTCPprocessing unit 102 and the RTP/RTCP processing unit 202 are connectedwith each other across the systems. A time stamp TS and a sequencenumber SN can be supplied from one RTP/RTCP processing unit to theother. In the operation in this embodiment, the write pointer WP and theread pointer RP, and the time stamp TS and the sequence number SN aresupplied from the operation system gateway unit to the standby systemgateway unit.

The audio processing unit 105 and the audio processing unit 205 areconnected to the TDM processing unit 106 and the TDM processing unit206, respectively. The TDM processing unit 106 and the TDM processingunit 206 are connected to the TDM exchange unit 30. The control unit 50is connected with the gateway unit 10 and the gateway unit 20, and theTDM exchange unit 30. The TDM exchange unit 30 is connected to thetelephone network 60. Also, to synchronize timing of audio processing, atiming signal generating unit 301 is connected to the TDM processingunit 106 and the TDM processing unit 206, the audio processing unit 105and the audio processing unit 205, the jitter buffer control unit 103and the jitter buffer control unit 203, and the RTP/RTCP processing unit102 and the RTP/RTCP processing unit 202.

The gateway unit 10 and the gateway unit 20 form a redundantconfiguration. Each of them is selectively set for the operation systemor for the standby system by a switch operation in accordance with aswitch signal from the control unit 50. Only the gateway unit (forexample, the gateway unit 10) set for the operation system is connectedto the packet network 70 where IP telephone services based on the VoIPtechnique are provided, via the packet network interface unit. The twogateway units 10 and 20 are constantly connected with the TDM exchangeunit 30 regardless of their setting for the operation system or thestandby system. The TDM exchange unit 30 is connected with the ordinarytelephone network 60 that transmits voice and sound in the form of TDMsignals, like a public subscription telephone network.

The control unit 50 is connected with the TDM exchange unit 30, thegateway unit 10 and the gateway unit 20, and the packet networkinterface units 40 and 41, and has a function of controlling theoperations of these units. In the case where a system switch request hasoccurred because of a system trouble or for maintenance, the controlunit 50 sends a system switch signal by automatic processing based on anexternal command operation or trouble detection. Also, the control unit50 sends out RTP session information of packetization information andthe like such as RTP packet size of audio data and the like to thegateway unit 10 and the gateway unit 20 in advance and causes them tohold the information. Also, at the time of system switching, the controlunit 50 sends out a system switch signal to the gateway unit 10 and thegateway unit 20 and changes their operations to the operation system orthe standby system. Moreover, the control unit 50 sets a physicaladdress and an IP address that are necessary to determine normality of areceiving packet or to assemble a transmitting packet, for the operationsystem or standby system gateway unit, and forms a communication-enablestate with the packet network 70.

The TDM exchange unit 30 is connected with the telephone network 60 andthus terminates its network transmission system. The TDM exchange unit30 has a function of supplying audio data extracted from a TDM signalfrom the telephone network 60 to both the gateway unit 10 and thegateway unit 20. The TDM exchange unit 30 includes the timing signalgenerating unit 301. The timing signal generating unit 301 generates aprocessing timing signal S1 that has a cycle equal to an integralmultiple of the frame clock cycle of the TDM signal supplied from thetelephone network 60 and that is common in the redundancy system. Thetiming signal generating unit 301 constantly supplies this processingtiming signal to each unit of both the gateway unit 10 and the gatewayunit 20.

The TDM processing unit 106 and the TDM processing unit 206 have afunction of integrating audio data of each channel from the TDM signalsupplied from the TDM exchange unit 30 and outputting this audio data tothe audio processing unit 105 and the audio processing unit 205 intiming based on the processing timing signal S1. The TDM signal is audiodata transmitted in plural speaking sessions, as shown in FIG. 2. Inthis embodiment, the integration timing to integrate and packetize audiodata of each channel from the TDM signal is synchronized with the timingof the frame clock (integral multiple) of the TDM signal.

The audio processing unit 105 and the audio processing unit 205 have afunction of performing audio processing such as echo erasing andcompression coding to the audio data from the TDM processing unit 106and the TDM processing unit 206 and supplying the processed audio datato the RTP/RTCP processing unit 102 and the RTP/RTCP processing unit202. The audio data is audio data integrated every cycle (for example,10 ms) of the processing timing signal S1, for each channel. The audioprocessing is performed to the audio data every cycle of the processingtiming signal S1, or every cycle that is equal to an integral multipleof that cycle, or every cycle divided with reference to that cycle. Theaudio data resulting from the audio processing is supplied in apredetermined RTP packet size to the RTP/RTCP processing unit 102 andthe RTP/RTCP processing unit 202 at predetermined intervalscorresponding to the size.

The RTP/RTCP processing unit 102 and the RTP/RTCP processing unit 202have a function of packetizing the audio data supplied from the audioprocessing unit 105 and the audio processing unit 205 to RTP packets andsupplying them to the IP processing unit 101 and the IP processing unit201. The audio data is taken in by the RTP packet size, for eachchannel. The RTP/RTCP processing unit 102 and the RTP/RTCP processingunit 202 also have a function of deciding the time stamp value TS andthe sequence number SN for each channel that should be set in the headerpart of the RTP packet, and a function of transmitting and receivingthem between the RTP/RTCP processing unit of the gateway unit set forthe operation system and the RTP/RTCP processing unit of the gatewayunit set for the standby system. In the RTP packet resulting frompacketizing, the audio data of each channel is stored in its payloadpart, and the time stamp value TS and the sequence number SN are storedin its header part.

The IP processing unit 101 and the IP processing unit 201 have afunction of taking, as their input, the RTP packet supplied from theRTP/RTCP processing unit 102 and the RTP/RTCP processing unit 202, thengenerating an IP packet in accordance with the packetization informationfrom the control unit 50, and outputting the IP packet to the packetnetwork interface unit 40 and the packet network interface unit 41.

The two gateway units 10 and 20 are commonly supplied with the same TDMsignal from the TDM exchange unit and execute processing in each unitsynchronously with the processing timing signal S1 based on the TDMsignal. As a result, the IP packets from the gateway unit 10 and thegateway unit 20 are perfectly the same and are sent out to the packetnetwork 70 at substantially the same intervals. Practically, since onlythe gateway unit set for the operation system is in thecommunication-enable state with the packet network 70 via the packetnetwork interface unit as described above, the IP packet from thegateway unit set for the operation system is transmitted to the packetnetwork 70 and the IP packet from the gateway unit set for the standbysystem is discarded at the packet network interface unit connectedthereto.

FIG. 3 shows input/output timing of audio data and packet in each of theoperation system and the standby system. In FIG. 3, to make theexplanation easier, it is assumed that one RTP packet and one IP packetare generated every cycle of the processing timing signal S1 in all thechannels. Here, the processing timing signal S1 is supplied to both thegateway unit of the operation system and the gateway unit of the standbysystem. Audio data of plural channels are inputted to the audioprocessing units of the operation system and the standby system everyclock of this processing timing signal S1. Similarly, audio data ofplural channels are inputted to the RTP/RTCP processing units of theoperation system and the standby system every clock of this processingtiming signal S1.

In the operation system, the time stamp value TS and the sequence numberSN are decided for each audio data of one channel. As shown in FIG. 3,the time stamp value TS=100 and the sequence number SN=10 are decidedfor the channel ch0. The time stamp value TS and the sequence number SNfor each channel are sent from the RTP/RTCP processing unit of theoperation system to the RTP/RTCP processing unit of the standby system.Both the RTP/RTCP processing units of the operation system and thestandby system store the same time stamp value TS and sequence number SNinto the RTP header, store audio data into the RTP payload part, andoutputs the RTP packet. The RTP packet is IP-packetized in both theoperation system and the standby system and then outputted from the IPprocessing units.

Outline of Operation in Packetizing

FIG. 4 shows an outline of operation to perform audio processing to theaudio data in a TDM signal received from the telephone network 60, thenpacketize the audio data and output it to the packet network. Since theRTP/RTCP processing units in the two systems perform processing toexchange the time stamp value TS and the sequence number SN with eachother, different operations are carried out in the operation system andthe standby system.

First, system switching is executed at a certain time point. It is nowassumed that the gateway unit 10 is set from the standby system to theoperation system, whereas the gateway unit 20 is set from the operationsystem to the standby system (step S1). The RTP/RTCP processing unit 102of the gateway unit 10 performs processing to packetize audio datasupplied from the audio processing unit 105 into an RTP packet andsupply it to the IP processing unit 101. In this packetization to theRTP packet, the time stamp value TS and the sequence number SN to bestored into the header part of the RTP packet are decided (step S2). Thetime stamp value TS and the sequence number SN are decided in such amanner that they continue from the time stamp value TS and the sequencenumber SN decided by the gateway unit 20, which used to be in theoperation system during the period when the gateway unit 10 was set forthe standby system.

Next, the RTP/RTCP processing unit 102 sends out the decided time stampvalue TS and sequence number SN toward the RTP/RTCP processing unit 202of the gateway unit 20 of the standby system, as the time stamp value TSand the sequence number SN (step S3). Then, the RTP/RTCP processing unit102 generates an RTP packet, stores the audio data into its payloadpart, and stores the previously decided time stamp value TS and sequencenumber SN into its header part, thus performing RTP packetizationprocessing (step S4).

Meanwhile, the RTP/RTCP processing unit 202 of the gateway unit 20 ofthe standby system similarly performs processing to packetize audio datasupplied from the audio processing unit 205 into an RTP packet andsupply it to the IP processing unit 201. At this time, in thepacketization to the RTP packet, the time stamp value TS and thesequence number SN sent out from the RTP/RTCP processing unit 102 of theoperation system are used as the time stamp value TS and the sequencenumber SN to be stored in the header part of the RTP packet. TheRTP/RTCP processing unit 202 generates an RTP packet, stores the audiodata into its payload part, and stores the time stamp value TS and thesequence number SN decided in the operation system, into the headerpart, thus performing RTP packetization processing (step S5).

The above processing in the RTP/RTCP processing unit 102 of theoperation system (steps S2 to S4) and the processing in the RTP/RTCPprocessing unit 202 of the standby system (step S5) are repeated everytime an RTP packet is generated. Since the time stamp value TS and thesequence number SN take consecutive values, the time stamp value TS andthe sequence number SN need not necessarily be sent out each time fromthe operation system to the standby system, depending on the case.

In the case where system switching is executed again later, it is thenassumed that the gateway unit 10 is set in turn from the operationsystem to the standby system, whereas the gateway unit 20 is set fromthe standby system to the operation system (step S6). The RTP/RTCPprocessing unit 202 of the gateway unit 20 performs processing similarto the above steps S2 to S4 (steps S7 and S8). Thus, the same packetsthat are perfectly synchronized with each other in the two systems canbe outputted.

Outline of Operation in Forming TDM Signal

With reference to FIG. 1 again, an outline of operation to synchronizethe processing in the operation system and the processing in the standbysystem with respect to the processing perform audio processing to theaudio data in a packet received from the packet network, then form a TDMsignal and output it to the telephone network will be described. In theexample shown in FIG. 1, it is assumed that, of the gateway unit 10 andthe gateway unit 20 forming a redundancy configuration, the gateway unit10 is used as the operation system and the gateway unit 20 is used asthe standby unit.

An arriving packet from the packet network 70 is inputted to the packetnetwork interface unit 40. The packet network interface unit 40 outputsthe inputted packet to the operation system packet selecting unit 100.The packet network interface unit 40 also duplicates the inputted packetand outputs the same packet to the standby system packet selecting unit200 by using the receiving packet confounding line PL. For the packetnetwork interface unit 40 and the packet network interface unit 41,system switching is not carried out at the same time as for the gatewayunits. An input packet from the packet network 70 is constantlyoutputted to both the operation system packet selecting unit 100 and thestandby system packet selecting unit 200.

The IP processing unit 101 and the IP processing unit 201 select only apacket that has arrived at the local redundancy gateway system, from IPpackets inputted from the packet selecting unit 100 set for theoperation system and the packet selecting unit 200, and output theselected packet to the RTP/RTCP processing unit 102 and the RTP/RTCPprocessing unit 202. The RTP/RTCP processing unit 102 and the RTP/RTCPprocessing unit 202 output the time stamp and the sequence number SN ofthe inputted packet to the jitter buffer control unit 103 and the jitterbuffer control unit 203, and output the audio data to the jitter buffer104 and the jitter buffer 204.

In writing to the jitter buffer 104 and the jitter buffer 204, the audiodata are inputted in the state where arrival fluctuation or packetreplacement in the packet network has occurred. Next, in reading fromthe jitter buffer 104 and the jitter buffer 204, the audio data areoutputted to the audio processing unit 105 and the audio processing unit205 in timing that meets the audio processing timing based on theprocessing timing signal S1. The audio processing unit 105 and the audioprocessing unit 205 carry out audio processing such as data generationfor echo erasing processing, and encoding and decoding processing, andoutput the audio data to the TDM processing unit 106 and the TDMprocessing unit 206 in timing based on the processing timing signal S1.The TDM processing unit 106 and the TDM processing unit 206 output theaudio data grouped by audio processing unit timing to the TDM exchangeunit 30, as time-division multiplex data using audio sampling timing asframe timing. TDM exchange unit 30 outputs the TDM signal of theoperation system gateway unit, of TDM signals from the gateway unit 10and the gateway unit 20, to the telephone network 60 in accordance withan input signal from the control unit 50. On the other hand, the TDMsignal of the standby system gateway unit is discarded at the TDMexchange unit 30.

Details of Operation in Forming TDM Signal

The detailed operation of the redundancy gateway system will bedescribed hereinafter with reference to FIG. 5 to FIG. 8. Here, theprocessing timing signal S1, processing timing numbers #1 to #11, anddata input timing to the jitter buffer 104 and the jitter buffer 204refer to the same timings in the cases shown in FIG. 5 to FIG. 8. It isassumed that the jitter buffer 104 and the jitter buffer 204 operate ascyclic buffers.

FIG. 5 shows an outline of a writing operation to the jitter buffer 104and the jitter buffer 204. The RTP packet is inputted to the RTP/RTCPprocessing unit 102 and the RTP/RTCP processing unit 202 in the statewhere arrival fluctuation or packet replacement in the packet networkhas occurred, and the data is inputted to the jitter buffer 104 and thejitter buffer 204 in the similar state. The jitter buffer 104 and thejitter buffer 204 divide their memory area into each audio processingunit and append a pointer (address) to each area for management. Thismakes the buffer management easier at the time of reading. Hereinafter,to make the explanation easier, a case will be described where oneinputted packet is one audio processing unit and the jitter buffer 104and the jitter buffer 204 have eight areas.

The jitter buffer control unit 103 of the operation system receives thetime stamp and the sequence number SN as identification information of apacket from the RTP/RTCP processing unit 102, and decides a writepointer for the operation system jitter buffer 104 in accordance withthe result of comparison with the time stamp and the sequence number SNof the previously received packet identification information. Here, thewrite pointer is decided in such a manner that the data order in thejitter buffer becomes consecutive. This enables the pointer at the timeof reading to have consecutive values and also enables easier readingcontrol.

In the chart shown in FIG. 5, the data inputted immediately after theprocessing timing number #5 has a sequence number SN=15, which is notconsecutive from the sequence number SN=13 of the previously inputteddata. This implies that a packet has been discarded or the packet orderhas been replaced in the packet network 70.

In this case, on the assumption that data is written consecutively tothe operation system jitter buffer 104 in the order of the sequencenumber SN of packets, if there is a free area in which the input datacan be written, the pointer value is decided as a write pointer, leavinga writing area for the data situated between the previously inputtedpacket and the present packet to carry out writing. Therefore, in thiscase, the write pointer WP for the data inputted immediately after theprocessing timing number #5 is WP=0 instead of WP=7, which is acquiredby adding 1 to the write pointer WP=6 for the previously inputted data.Thus, the pointer value is decided leaving the area of WP=7 as a writingarea of SN=14. The data that is inputted next has SN=16 and WP=1. Thesubsequently inputted data has SN=14. In this case, it is determinedthat the input packet can be written if it is not a packet with timingafter being read from the operation system jitter buffer 104. The writepointer is decided to WP=7 and then writing is carried out.

As a result of the above operation, the data are written into the jitterbuffer 104 with consecutive data order. The write pointer decided in theoperation system is transferred to the standby system at the same time,and it is decided as the write pointer for the standby system jitterbuffer 204. As the write pointer is thus transferred from the operationsystem to the standby system, the data writing state of the operationsystem jitter buffer 104 and the data writing state of the standbysystem jitter buffer 204 can be made perfectly coincident with eachother.

FIG. 6 shows an outline of a reading operation from the jitter buffer104 and the jitter buffer 204. The jitter buffer 104 and the jitterbuffer 204 are caused to operate with a predetermined quantity ofpackets accumulated that are necessary to absorb arrival fluctuation ofpackets and packet replacement occurring in the packet network 70. Thejitter buffer 104 and the jitter buffer 204 are caused to operate insuch a manner that the data read out from them become continuous datastrings. Therefore, at the start of speaking, the read pointer RP isdecided and operates with spacing from the write pointer WP by an amountequivalent to a pointer value corresponding to the predeterminedquantity that should be accumulated in the jitter buffer 104.

Moreover, since data have been written to the jitter buffer 104 and thejitter buffer 204 in such a manner that the data order becomesconsecutive as described above, the read pointer in the next processingtiming is decided by adding 1 every time data is read out in accordancewith the processing timing S1. The read pointer decided in the operationsystem gateway unit 10 is transferred to the standby system gateway unit20 at the same time and is decided as the read pointer for the standbysystem jitter buffer 204. As the read pointer is thus transferred fromthe operation system gateway unit 10 to the standby system gateway unit20, the contents of output data of the operation system jitter buffer104 and the standby system jitter buffer 204 can be made perfectlycoincident with each other. Also, as the data is read out from theoperation system jitter buffer 104 and the standby system jitter buffer204 in accordance with the processing timing signal S1, the timing ofdata output from the jitter buffer 104 in the operation system gatewayunit 10 and timing of data output from the jitter buffer 204 in thestandby system gateway unit 20 can be perfectly synchronized with eachother.

With reference to the bottom of FIG. 6, the state of data accumulationin the operation system jitter buffer 104 and the standby system jitterbuffer 204 can be seen. If the processing timing numbers are referred totogether with the processing timing numbers in FIG. 5, the state ofwriting and reading data to and from the operation system jitter buffer104 and the standby system jitter buffer 204, and the operating state ofeach pointer can be clarified.

FIG. 7 shows an operation in the case where the write pointer and theread pointer are not transferred between the two systems. Here, it isassumed that a maintenance serviceman incorporates the standby systemgateway unit 20 during the operation of the operation system gatewayunit 10. The processing timing signal S1, the processing timing numbers,and the timing of input data to the jitter buffer 104 and the jitterbuffer 204 are the same as in the above-described cases shown in FIG. 5and FIG. 6. It is also assumed that the predetermined quantity necessaryto absorb arrival fluctuation of packets and packet replacementoccurring in the packet network 70 is 4 packets, and that silent data isset as initial data in the jitter buffer 104 and the jitter buffer 204.

First, it is assumed that the standby system gateway unit 20 isincorporated and starts operating in timing of the processing timingnumber #1. In the standby system gateway unit 20, data (sequence numberSN=10) inputted immediately after the processing timing number #1 iswritten from the initial write pointer WP=0 of the buffer. Thesubsequently inputted data operates similarly to the above-describedwriting operation. The data is inputted in a burst between theprocessing timing numbers #2 and #4. At the time point of the processingtiming #4, since the predetermined quantity (4 packets) necessary toabsorb arrival fluctuation of packets and packet replacement occurringin the packet network is satisfied, data reading starts at theprocessing timing number #5.

Meanwhile, in the operation system gateway unit 10, the data (sequencenumber SN=10) inputted immediately after the processing timing number #1is written from the write pointer WP=3, which is a halfway point, andits reading starts at the processing timing number #6.

As a result, the output data of the operation system jitter buffer 104and the output data of the standby system jitter buffer 204 are shiftedfrom each other. If system switching is executed between the operationsystem gateway unit 10 and the standby system gateway unit 20 in thisstate, data loss equivalent to one audio processing unit occurs.

FIG. 8 shows an operation in the case where the write pointer and theread pointer are transferred between the two systems. Here, it isassumed that a maintenance serviceman incorporates the standby systemgateway unit 20 during the operation of the operation system gatewayunit 10. The processing timing signal S1, the processing timing numbers,and the timing of input data to the jitter buffer 104 and the jitterbuffer 204 are the same as in the above-described cases shown in FIG. 5,FIG. 6 and FIG. 7.

In the case where the standby system gateway unit 20 is incorporated andstarts operating in timing of the processing timing number #1, data(sequence number SN=10) inputted immediately after the processing timingnumber #1 is written into the buffer from the write pointer WP=3 that istransferred and received from the operation system. The subsequentlyinputted data operates similarly to the above-described writingoperation. The data is inputted in a burst between the processing timingnumbers #2 and #4. At the time point of the processing timing #4, sincethe predetermined quantity necessary to absorb arrival fluctuation ofpackets and packet replacement occurring in the packet network issatisfied, data reading starts at the processing timing number #5. Atthis time, the read pointer transferred and received from the operationsystem gateway unit 10 is RP=2, and silent data, which initial data, isoutputted from the standby system jitter buffer 204. The read pointer ofthe processing timing number #6 is RP=3, and the previously written datawith the sequence number SN=10 is read out. Thus, the contents of theoutput data of the operation system jitter buffer 104 and the standbysystem jitter buffer 204 perfectly coincide with each other.

Also, the packet network interface unit 40 and the packet networkinterface unit 41 duplicate the received packet and output the packet ofthe same content to both the packet selecting unit 100 and the packetselecting unit 200 connected thereto. Thus, in the echo erasingprocessing by the audio processing unit 105 and the audio processingunit 205, optimum conditions for optimum echo erasing processing for aspeaking session are maintained in both the operation system and thestandby system.

Description of Effects and Advantages of First Embodiment

In the above-described first embodiment, as the redundancy gatewaysystem according to the invention is used, the series of processingincluding TDM processing, audio processing, RTP/RTCP processing and IPprocessing can be carried out in timing based on the frame clock of theTDM signal in both the gateway unit 10 and the gateway unit 20 formingthe duplex redundant configuration, and the same packets perfectlysynchronized in the two system can be outputted to the packet network70.

Also, as the time stamp value TS and the sequence number SN areexchanged between the two systems, identity and continuity of thesevalues can be guaranteed. Even in the case where system switching hasoccurred, the time stamp value TS and the sequence number SN can takeconsecutive values. In the receiver device of the communication partnervia the packet network 70, discontinuity of packets is not detected andthe communication is not affected by short interruption.

Moreover, a packet received from the packet network 70 is shared by boththe operation system and the standby system. Jitter buffer control iscarried out in accordance with the processing timing signal S1 generatedby the timing signal generating unit 301, and jitter buffer control iscarried out by transferring the write pointer and the read pointerbetween the operation system jitter buffer 104 and the standby systemjitter buffer 204. Thus, the contents of output data of the operationsystem jitter buffer 104 and the standby system jitter buffer 204 can bemade coincident with each other, and their output timing can besynchronized. This enables the same audio data that are perfectlysynchronized, to be outputted from the plural gateway units 10 and 20forming the redundant configuration to the telephone network 60.Therefore, the communication is not affected by short interruption orduplication of audio data when the operation system of the redundancysystem is switched.

Also, as optimum conditions for optimum echo erasing processing for acommunication session are maintained in both the operation system andthe standby system, the time required for setting the echo erasingprocessing in a state where normal echo erasure is possible, can beomitted and the speaking is not subject to the feeling of abnormality.

Modification of First Embodiment

In the above embodiment, the timing signal generating unit 301, whichgenerates a processing timing signal based on the clock of a TDM signal,is provided in the TDM exchange unit 30 outside of the gateway units 10and 20. However, such a function may be provided in the gateway unit 10and/or 20.

In the embodiment, such a processing timing signal is supplied to thegateway units of the two systems from the TDM exchange unit 30. However,a signal that provides processing timing may be incorporated in the TDMsignal itself, which is supplied from the TDM exchange unit 30 to thegateway units 10 and 20 of the two systems, thus perfectly synchronizingthe series of processing in the two systems.

In the embodiment, the processing timing signal S1 as a reference isgenerated on the basis of the clock of the TDM signal. However,reference timing having an arbitrary cycle supplied from within or fromoutside of the gateway units 10 and 20 may be used to perfectlysynchronize the series of processing in the two systems.

Also, in the first embodiment, the jitter buffer 104 and the jitterbuffer 204 are divided into areas corresponding to each audio processingunit, and a pointer corresponding to the sequence number given to apacket is appended to each area for management, and the write pointerand the read pointer are transferred from the operation system to thestandby system to synchronize output data. However, a pointercorresponding to the time stamp given to the packet instead of thesequence number may be appended for management, and the write pointerand the read pointer may be transferred from the operation system to thestandby system to synchronize output data.

Moreover, in the above first embodiment, one packet is used as one audioprocessing unit. However, as another modification of the invention, inthe case where an inputted packet has a longer audio packetization cycle(packet length) than the audio processing unit, the audio data may bedivided in accordance with the audio processing unit and the dividedaudio data may be managed by pointer. Alternatively, new identificationinformation may be added to realize synchronization, for example, bynewly appending a time stamp value TS to each of the divided audio dataand thus realizing synchronization between the two systems, or by newlyappending a sequence number SN to each of the divided audio data andthus realizing synchronization. On the other hand, in the case where aninputted packet has a shorter audio packetization cycle (packet length)than the audio processing unit, the audio data may be collectivelymanaged by pointer in accordance with the audio processing unit.Alternatively, new identification information may be appended to realizesynchronization, for example, by newly appending a time stamp value TSto each collective audio data and thus realizing synchronization, or bynewly appending a sequence number SN to each collective audio data andthus realizing synchronization.

Second Embodiment

FIG. 9 shows a configuration of a redundancy gateway system and anetwork connected thereto according to a second embodiment. Here, theredundancy gateway system includes at least two gateway units 10 and 20that are provided between a packet network 160 and a packet network 261as packet networks forming a redundant configuration including apresent-use configuration and a spare configuration, and a telephonenetwork 60 as a TDM network, and that are configured in a multiplexmanner to form plural systems. The redundancy gateway system alsoincludes a control unit 50, and a TDM exchange unit 30.

In the second embodiment, the terms “present-use” and “spare” are usedinstead of “operation system” and “standby system” used in the firstembodiment. This is based on the assumption that the two systemsincluding the packet networks and the gateway units are simultaneouslyoperable and that the two systems take an operation form to performredundant processing of packets of the same contents in different routesand in parallel.

The gateway unit 10 and the gateway unit 20 are connected to the packetnetwork 160 and the packet network 261, which form a present-useconfiguration and a spare configuration, respectively. The gateway unit10 sends and receives packets to and from the packet network 160. Thegateway unit 20 sends and receives packets to and from the packetnetwork 261. For example, if the packet network 160 is configured forpresent use and the packet network 261 is configured for spare use as aninitial state, the gateway unit 10 is set for present use and thegateway unit 20 is set for spare use.

In the case where a system switch request is made because of systemtrouble or for maintenance services, the control unit 50 performs asystem switching operation by automatic processing based on a commandoperation or trouble detection from outside. Specifically, the controlunit 50 supplies a control signal to the gateway units 10 and 20 andselectively sets each of the gateway units 10 and 20 for present use orfor spare use. The control unit 40 also sets packetization informationsuch as packet size and communication destination information in RTPpacketization of audio data, and a physical address and IP addressnecessary for connection to the packet network 160 and the packetnetwork 261, as presetting for the gateway units 10 and 20.

The TDM exchange unit 30 is connected to the telephone network 60 and isconstantly connected with the two gateway units 10 and 20 irrespectiveof the setting for present use or for spare use. However, the TDMexchange unit 30 selects audio data of the present-use gateway unit,which is one of the gateway unit 10 and the gateway unit 20, inaccordance with the setting by the control unit 40, and outputs theselected audio data to the telephone network 60. The TDM exchange unit30 also includes a timing signal generating unit 301, which supplies acommon timing signal S1 to the gateway unit 10 and the gateway unit 20.

The gateway unit 10 and the gateway unit 20 have the same internalconfiguration. The gateway unit 10 includes a packet network interfaceunit 300, an IP processing unit 311, an RTP/RTCP processing unit 302, alocal system receiving buffer 303, a remote system receiving buffer 304,a receiving buffer control unit 305, a jitter buffer control unit 306, ajitter buffer 307, an audio processing unit 308, and a TDM processingunit 309. Similarly, the gateway unit 20 includes a packet networkinterface unit 400, an IP processing unit 401, an RTP/RTCP processingunit 402, a local system receiving buffer 403, a remote system receivingbuffer 404, a receiving buffer control unit 405, a jitter buffer controlunit 406, a jitter buffer 407, an audio processing unit 408, and a TDMprocessing unit 409.

The gateway unit 10 sends and receives packets to and from the packetnetwork 160 through the packet network interface unit 300. The gatewayunit 20 sends and receives packets to and from the packet network 261through the packet network interface unit 400. The gateway units 10 and20 constantly maintain the communication-enable state to theirrespective packet networks irrespective of the setting for present useor for spare use.

The packet network interface units 300 and 400 are connected with the IPprocessing units 311 and 401, respectively. The IP processing units 311and 401 are connected with the RTP/RTCP processing units 302 and 402,respectively. The RTP/RTCP processing units 302 and 402 have a functionof duplicating a local system receiving packet. The RTP/RTCP processingunit 302 is connected with the local system receiving buffer 303 andalso connected with the remote system receiving buffer 404 via areceiving packet confounding line PL, and outputs packets of the samecontents to both receiving buffers. Similarly, the RTP/RTCP processingunit 402 is connected with the local system receiving buffer 403 andalso connected with the remote system receiving buffer 304 via areceiving packet confounding line PL, and outputs packets of the samecontents to both receiving buffers. The RTP/RTCP processing units 302and 402 are also connected with the audio processing units 308 and 408,respectively.

The jitter buffer control units 306 and 406 are connected with eachother across the systems, and perform an operation to synchronize thejitter buffer operation by supplying a write pointer WP and a readpointer RP that are commonly used in the redundancy gateway system, fromone jitter buffer control unit to the other.

The RTP/RTCP processing units 302 and 402 are connected with each otheracross the systems, and perform an operation to synchronize RTP/RTCPprocessing by supplying the time stamp TS and the sequence number SNfrom one RTP/RTCP processing unit to the other.

The jitter buffers 307 and 407 are connected with the audio processingunits 308 and 408. The audio processing units 308 and 408 are connectedwith the TDM processing units 309 and 409. The TDM processing units 309and 409 are connected to the TDM exchange unit 30. The control unit 50is connected with the gateway unit 10 and the gateway unit 20, and withthe TDM exchange unit 30. The TDM exchange unit 30 is connected with thetelephone network 60.

The IP processing units 311 and 401, the RTP/RTCP processing units 302and 402, the jitter buffer control units 306 and 406, the jitter buffers307 and 407, the audio processing units 308 and 408, and the TDMprocessing units 309 and 409 have the similar functions to those in thefirst embodiment. These units are supplied with a timing signal S1 fromthe timing signal generating unit 301 of the TDM exchange unit 30 andperform synchronized operations in audio processing timing in accordancewith the timing signal S1. Thus, the jitter buffer operation, and theoperations related to synchronization of RTP/RTCP processing and audioprocessing timing are similar to those in the first embodiment.

The local system receiving buffer 303 and the remote system receivingbuffer 304 included in the gateway unit 10 are connected with thereceiving buffer control unit 305 and supply audio data from the localsystem packet network 160 and audio data from the remote system packetnetwork 261 received through the receiving packet confounding line PL.The receiving buffer control unit 305 is also connected with the localsystem receiving buffer 303 and the remote system receiving buffer 304in order to control writing and reading.

The local system receiving buffer 403 and the remote system receivingbuffer 404 included in the gateway unit 20 are connected with thereceiving buffer control unit 405 and supply audio data from the localsystem packet network 261 and audio data from the remote system packetnetwork 160 received through the receiving packet confounding line PL.Also, the receiving buffer control unit 405 is connected with the localsystem receiving buffer 403 and the remote system receiving buffer 404,and controls writing to and reading from these buffers. The receivingbuffer control units 305 and 405 are connected with the jitter buffercontrol units 306 and 406, respectively and with the jitter buffers 307and 407, respectively and supply audio data received by them. Thereceiving buffer control unit 305 and the receiving buffer control unit405 are connected with each other via a receiving buffer control signalline CL across the systems, and perform synchronization of the localsystem receiving buffers 303 and 403 and the remote system receivingbuffers 304 and 404 by supplying a buffer pointer BP from one receivingbuffer control unit to the other.

FIG. 10 to FIG. 13 show operations of the redundancy gateway systemaccording to the second embodiment, in the form of time charts with thehorizontal axis representing time. The operations of the redundancygateway system will be described hereinafter, properly referring to FIG.10 to FIG. 13 and the component elements shown in the block diagram ofFIG. 9.

It is assumed that the redundancy gateway system receives the samepacket from the packet network 160 and the packet network 261 inparallel, then converts the packet to audio data in the form of TDMsignal and outputs it to the telephone network 60.

The packet network interface units 300 and 400 receive packets from thepacket network 160 and the packet network 261, receive only a packetwith a local system physical address that is preset by the control unit50, and supply the received packet to the IP processing units 311 and401. The IP processing-units 311 and 401 receive only a packet with alocal system IP address that is preset by the control unit 50, of thesupplied packets, then confirm normality of header information and datain accordance with the need, and supply only a valid packet to theRTP/RTCP processing units 302 and 402.

The RTP/RTCP processing units 302 and 402 extract packet discriminationinformation from the supplied packet, that is, information such as portnumber, sequence number, time stamp, and synchronization sourceidentifier (SSRC), and combine these with the audio data of the payloadpart to generate audio data. Moreover, the RTP/RTCP processing unit 302supplies the generated audio data to the local system receiving buffer303 and also supplies the audio data to the remote system receivingbuffer 404 via the receiving packet confounding line PL. Similarly, theRTP/RTCP processing unit 402 supplies the generated audio data to thelocal system receiving buffer 403 and also supplies the audio data tothe remote system receiving buffer 304 connected via the receivingpacket confounding line PL.

Writing Operation to Receiving Buffer

FIG. 10 shows a writing operation to the local system receiving buffers303 and 403 and the remote system receiving buffers 304 and 404 by thereceiving buffer control units 305 and 405. Here, each of the localsystem receiving buffers 303 and 403, the remote system receivingbuffers 304 and 404, and the receiving buffer control units 305 and 405,has a four-side memory configuration with individual pointers appointedthereto. The actual memory configuration should be decided by networkconditions and so on.

First, in timing t0, audio data (SN=10) inputted from the RTP/RTCPprocessing unit 302 to the local system receiving buffer 303 in thepresent-use gateway unit 10 is written to a pointer 0 in the localsystem receiving buffer 303 in accordance with write pointer managementby the receiving buffer control unit 305. Meanwhile, the same audio data(SN=10) is inputted from the RTP/RTCP processing unit 302 to the remotesystem receiving buffer 404 via the receiving packet confounding linePL. At the same time, the write pointer of the local system receivingbuffer 303 is transferred from the present-use gateway unit 10 to thespare gateway unit 20. In response to this, the audio data (SN=10) iswritten to a pointer 0 in the remote system receiving buffer 404 of thespare gateway unit 20 in accordance with write pointer management by thereceiving buffer control unit 405 of the spare gateway unit 20.

Next, in timing t1, audio data (SN=11) inputted to the local systemreceiving buffer 303 is similarly written to a pointer 1 in the localsystem receiving buffer 303. The same audio data (SN=11) inputted to theremote system receiving buffer 404 is similarly written to a pointer 1in the remote system receiving buffer 404. Subsequently, the similaroperation is carried out and the same audio data is written to the samepointer in the local system receiving buffer 303 and the remote systemreceiving buffer 404.

Meanwhile, in parallel to the above operation, in timing t0, the audiodata (SN=10) inputted from the RTP/RTCP processing unit 402 of the sparegateway unit 20 is supplied to the local system receiving buffer 403 andalso supplied to the remote system receiving buffer 304 via thereceiving packet confounding line PL. The audio data (SN=10) supplied tothe local system receiving buffer 403 is written to a pointer 0 in thelocal system receiving buffer 403 in accordance with write pointermanagement by the receiving buffer control unit 405 of the spare gatewayunit 20. The audio data (SN=10) supplied to the remote system receivingbuffer 304 is written to a pointer 0 in the remote system receivingbuffer 304 in accordance with write pointer management by the receivingbuffer control unit 305 of the present-use gateway unit 10.Subsequently, the similar operation is carried out as in the operationwith respect to the audio data inputted from the RTP/RTCP processingunit 302 of the present-use gateway unit 10.

However, in the second embodiment, each write pointer is transferredfrom the present-use gateway unit 10 to the spare gateway unit 20, thusrealizing uniformity of the operation management. That is, the receivingbuffer control unit 305 of the present-use gateway unit 10 decides andcontrols, on its own, the write pointer in the local system receivingbuffer 303 and the remote system receiving buffer 304. On the otherhand, the receiving buffer control unit 405 of the spare gateway unit 20controls the write pointer in the local system receiving buffer 403 andthe remote system receiving buffer 404 in accordance with the writepointer transferred from the present-use gateway unit 10.

Reading Operation from Receiving Buffer

FIG. 11 shows a reading operation from the local system receiving buffer303 and the remote system receiving buffer 304 of the present-usegateway unit 10 by the receiving buffer control unit 305. Here, thereceiving buffer control unit 305 constantly monitors whether each ofthe local system receiving buffer 303 and the remote system receivingbuffer 304 holds audio data or not. If they hold audio data, they arecontrolled to perform a reading operation each time. The reading targetbuffer and the read pointer are centrally decided by the receivingbuffer control unit 305 of the present-use gateway unit 10. Also, thereading operation from the receiving buffers is controlled by thereceiving buffer control unit 305 using a read enable signal so thatreading is not simultaneously carried out from both the local systemreceiving buffer 303 and the remote system receiving buffer 304. In themiddle stage in FIG. 11, read enable signals to the local systemreceiving buffer 303 and the remote system receiving buffer 304 andaudio data strings to be outputted are shown.

First, immediately after timing t0, and after writing of the audio data(SN=10) inputted to the local system receiving buffer 303, into thelocal system receiving buffer 303, is completed, it is detected by thereceiving buffer control unit 305 that the audio data is held in thelocal system receiving buffer 303. The audio data is read out from thelocal system receiving buffer 303 and supplied to the receiving buffercontrol unit 305. After that, also the audio data (SN=10) inputted theremote system receiving buffer 304 is similarly read out from the remotesystem receiving buffer 304 and supplied to the receiving buffer controlunit 305. Here, the audio data supplied to the receiving buffer controlunit 305 is supplied from both the packet network 160 and the packetnetwork 261. Therefore, processing with a data rate that is twice higheris necessary. In the actual circuit, the circuit configuration thatmultiplies the data bus is employed to improve the processing rate.

The receiving buffer control unit 305 extracts packet discriminationinformation from the supplied audio data, that is, information such asport number, sequence number, time stamp, and synchronization sourceidentifier (SSRC), and determines whether the audio data is the same asthe audio data that has been supplied in advance. If it is determinedthat the audio data is the same as the audio data that has been suppliedin advance, the audio data is discarded as duplicate audio data. Here,the audio data supplied in advance that is necessary for suchdetermination, of the audio data received in the past, is the audio datareceived at a time preceding the present time point by at least“α+β+maximum delay time in buffer reading”, where the arrivalfluctuation time in the packet network 160 is ±α hours and the arrivalfluctuation time in the packet network 261 is ±β hours.

In the bottom of FIG. 11, audio data outputted as the result of theabove-described discard processing in the receiving buffer control unit305 is shown. Only the audio data read out first from the local systemreceiving buffer 303 or the remote system receiving buffer 304 issupplied to the jitter buffer 307 and the jitter buffer control unit 306on the subsequent stage as a valid audio data.

In FIG. 11, the operation of the present-use gateway unit 10 isdescribed. Also the operation of the spare gateway unit 20 is carriedout basically in a similar manner. However, in reading from the localsystem receiving buffer 403 and the remote system receiving buffer 404in the spare gateway unit 20, the reading target buffer and the readpointer decided by the receiving buffer control unit 305 with respect tothe local system receiving buffer 303 and the remote system receivingbuffer 304 in the above-described present-use gateway unit 10 are sentto the receiving buffer control unit 405 via the receiving buffercontrol signal line CL. As the receiving buffer control unit 405receives the reading target buffer and the read pointer, the receivingbuffer control unit 405 controls the reading operation from the remotesystem receiving buffer 404 and the local system receiving buffer 403synchronously with the reading operation in the present-use gateway unit10. In this case, reading from the remote system receiving buffer 404 iscarried out after the read pointer in the local system receiving buffer303 of the present-use gateway unit 10 is substituted for the readpointer in the remote system receiving buffer 404 of the spare gatewayunit 20. Reading from the local system receiving buffer 403 is carriedout after the read pointer in the remote system receiving buffer 304 ofthe present-use gateway unit 10 is substituted for the read pointer inthe local system receiving buffer 403 of the spare gateway unit 20. Bythe above operation, the same audio data that are perfectly synchronizedare supplied to the jitter buffer control unit 306 and the jitter buffer307 in the present-use gateway unit 10, and to the jitter buffer controlunit 406 and the jitter buffer 407 in the spare gateway unit 20.

FIG. 12 shows an operation in the case where the write/read pointer ofthe receiving buffer is “not transferred” through the receiving buffercontrol signal line CL when the spare gateway unit 20 is newlyincorporated during the operation of the present-use gateway unit 10.Here, it is assumed that the spare gateway unit 20 is incorporated inthe state where audio data (SN=19) that is not read out is held in thelocal system receiving buffer 303 of the present-use gateway unit 10.

First, immediately after timing t10, inputted audio data (SN=20) iswritten to a pointer 2 in the local system receiving buffer 303 of thepresent-use gateway unit 10. Similarly, the audio data (SN=20) is alsoinputted via the receiving packet confounding line PL to the remotesystem receiving buffer 404 of the spare gateway unit 20, which has beenincorporated before, and the audio data is written to an initial pointer0.

After writing of the audio data (SN=20) is completed, in the case whereaudio data is to be read out from the local system receiving buffer 303and the remote system receiving buffer 404, the audio data (SN=19) heldin the local system receiving buffer 303 is read out first in thepresent-use gateway unit 10. On the other hand, in the spare gatewayunit 20, the audio data (SN=20) is read out. That is, the same audiodata that are perfectly synchronized are not supplied to the jitterbuffer control unit 306 and the jitter buffer 307 in the present-usegateway unit 10, and to the jitter buffer control unit 406 and thejitter buffer 407 in the spare gateway unit 20. As a result,synchronization of the jitter buffers described in the first embodimentcannot be realized.

FIG. 13 shows an operation in the case where the write/read pointer ofthe receiving buffer is “transferred” through the receiving buffercontrol signal line when the spare gateway unit 20 is newly incorporatedduring the operation of the present-use gateway unit 10. Here, as in thecase of FIG. 12, it is assumed that the spare gateway unit 20 isincorporated in the state where the audio data (SN=19) that is not readout is held in the local system receiving buffer 303 of the present-usegateway unit 10.

First, immediately after timing t10, inputted audio data (SN=20) iswritten to a pointer 2 in the local system receiving buffer 303 of thepresent-use gateway unit 10. Similarly, the inputted audio data (SN=20)is written via the receiving packet confounding line PL to a pointer 2in the remote system receiving buffer 404 of the spare gateway unit 20,which has been incorporated before, in accordance with the write pointervalue 2 inputted via the receiving buffer control signal line CL.

After writing of the audio data (SN=20) is completed, in the case whereaudio data is to be read from the local system receiving buffer 303 andthe remote system receiving buffer 404, the audio data (SN=19) held inthe local system receiving buffer 303 is read out first in thepresent-use gateway unit 10. On the other hand, in the spare gatewayunit 20, a free area of pointer 1 is read out in accordance with theread pointer value 1 transferred thereto. However, the output data whereno audio data is written is made silent data, thereby supplying datahaving no influence on the audio processing unit 408 on the subsequentstage.

Next, in the case where the audio data (SN=20) is read out from thelocal system receiving buffer 303, the audio data (SN=20) is also readout from the remote system receiving buffer 404. That is, the same audiodata that are perfectly synchronized are supplied to the jitter buffercontrol unit 306 and the jitter buffer 307 in the present-use gatewayunit 10 and to the jitter buffer control unit 406 and the jitter buffer407 in the spare gateway unit 20. As a result, as described in the firstembodiment, the jitter buffer control units 306 and 406 that control thejitter buffer 307 and the jitter buffer 407, respectively, the audioprocessing units 308 and 408, and the TDM processing units 309 and 409can perform processing perfectly synchronously in accordance with thereference timing signal s1.

Description of Effects and Advantages of Second Embodiment

In the above second embodiment, the gateway units 10 and 20 form acommunication-enable state to the packet network 160 and the packetnetwork 261 of the redundant configuration, partly in place of theconfiguration described in the first embodiment. Each of the gatewayunits 10 and 20 extracts and commonly holds a series of valid packetsthat are not duplicate, from all the packets including the packetsreceived by the remote system.

In the configuration of the first embodiment, in the case where thepacket network 160 and the packet network 261 form the redundantconfiguration and system switching is carried out between them, therestill is a difference in timing between such system switching and systemswitching between gateway units forming a redundant configuration, andloss of a packet or packets cannot be avoided. On the other hand, in theconfiguration of the second embodiment, even in system switchingincluding the packet network 160 and the packet network 261 forming theredundant configuration, loss of receiving packets does not occur andsystem switching can be carried out without any short interruption.

Also, since each of the gateway units 10 and 20 extracts and commonlyholds a series of valid packets from all the packets including thepackets received by the remote system, system switching between thepacket network 160 and the packet network 261 forming the redundantconfiguration, and system switching between the gateway units 10 and 20forming the redundant configuration can be separately carried out.Therefore, system switching can be easily carried out without using aspecial network switching device and without causing any shortinterruption. Such effects not only improve the maintenance property ofthe gateway units but also significantly improve the maintenanceproperty of the packet networks because the gateway units need not beaware of the present use or spare use of the packet networks.

Modification of Second Embodiment

In the above second embodiment, the receiving buffer control unit 305extracts packet discrimination information, that is, information such asport number, sequence number, time stamp, and synchronization sourceidentifier (SSRC), from the audio data supplied from the receivingbuffer, and determines whether the audio data is the same as the audiodata that has been supplied before. If it is determined that it is theaudio data that has been inputted before, the audio data is discarded asduplicate audio data. However, such functions may be provided in thejitter buffer control units 306 and 406.

The jitter buffer control units 306 and 406 may extract packetdiscrimination information, that is, information such as port number,sequence number, time stamp, and synchronization source identifier(SSRC), from the audio data supplied from the receiving buffer, anddetermine whether the audio data is the same as the audio data that hasbeen supplied before and written to the jitter buffers. If it isdetermined that it is the audio data that has been written to the jitterbuffers, the jitter buffer control units 306 and 406 may determine theaudio data to be duplicate audio data and control the write enablesignal of the jitter buffers into a non-write state.

In the above embodiments, the gateway units that house a telephone unitand perform audio processing are described as an example. However, theinvention is broadly applicable to cases where system switching withoutshort interruption is necessary in a redundancy gateway system thatcarries out data communications using not only audio but also a packetnetwork.

Also, in the above embodiments, the communication form in which transferis carried out on the IP protocol is described as an example. However,the invention is applicable not only to cases where the IP protocol isused as the transfer protocol, but also to cases where other packetprotocols such as ATM (Asynchronous Transfer Mode) and FR (Frame Relay)are used.

Moreover, in the above embodiments, one audio channel is described.However, the redundancy gateway system according to the invention isalso applicable to gateway units that process plural channels.

This application is based on Japanese Patent Applications Nos.2006-342458 and 2007-197425 which are hereby incorporated by reference.

1. A redundancy gateway system, including a plurality of gateway units,configured in a multiplex manner between a packet network and a TimeDivision Multiplexing (TDM) network, and which performs TDM conversionprocessing to a plurality of packets supplied from the packet network,by the gateway units, and supplies a resulting TDM signal to the TDMnetwork, the redundancy gateway system comprising: a same packet supplyunit that generates a duplicate of the packet and thus supplies packetsof the same content to the plurality of gateway units; a common writepointer generating unit that generates, for each of the packets, acommon write pointer corresponding to identification informationappended to the packet; and a selective supply unit that selectivelyswitches one of the plurality of gateway units and supplies only a TDMsignal acquired from the one gateway unit to the TDM network; whereineach of the plurality of gateway units includes at least one jitterbuffer, a unit that generates a read pointer for the jitter buffer, anda jitter buffer control unit that writes, for each supplied packet, thepacket into the jitter buffer in accordance with the common writepointer corresponding to the packet, and sequentially reads out awritten packet from the jitter buffer in accordance with the jitterbuffer read pointer and provides it for the TDM conversion processing;wherein the common write pointer generating unit and the read pointergenerating unit are provided in each of the plurality of gateway units;and wherein only one gateway unit, corresponding to an operation commandgenerates the write pointer and the read pointer and commonly suppliesthem to all the gateway units.
 2. A redundancy gateway system thatincludes a plurality of gateway units configured in a multiplex mannerbetween a packet network and a TDM network, and which performs a TimeDivision Multiplexing (TDM) conversion processing to a plurality ofpackets supplied from the packet network, by the gateway units, andsupplies a resulting TDM signal to the TDM network, the redundancygateway system comprising: a same packet supply unit that generates aduplicate of the packet and thus supplies packets of the same content tothe plurality of gateway units; a common write pointer generating unitthat generates, for each of the packets, a common write pointercorresponding to identification information appended to the packet; anda selective supply unit that selectively switches one of the pluralityof gateway units and supplies only a TDM signal acquired from the onegateway unit to the TDM network; wherein each of the plurality ofgateway units includes at least one jitter buffer, a unit that generatesa read pointer for the jitter buffer, and a jitter buffer control unitthat writes, for each supplied packet, the packet into the jitter bufferin accordance with the common write pointer corresponding to the packet,and sequentially reads out a written packet from the jitter buffer inaccordance with the jitter buffer read pointer and provides it for theTDM conversion processing; further comprising a processing timing signalgenerating unit that generates a common processing timing signal with apredetermined cycle, wherein all the plurality of gateway units carryout writing and reading operations to and from their own jitter buffersthat they have, synchronously with the common processing timing signal;wherein the common write pointer generating unit and the read pointergenerating unit are provided in each of the plurality of gateway units;and wherein only one gateway unit corresponding to an operation commandgenerates the write pointer and the read pointer and commonly suppliesthem to all the gateway units.
 3. A redundancy gateway system whichincludes a plurality of gateway units configured in a multiplex mannerbetween a plurality of packet networks configured in a multiplex mannerand a Time Division Multiplexing (TDM) network, and which performs TDMconversion processing to a plurality of packets supplied from the packetnetworks, by the gateway units, and supplies a resulting TDM signal tothe TDM network, the redundancy gateway system comprising: a commonwrite pointer generating unit that generates, for each of the packets, acommon write pointer corresponding to identification informationappended to the packet; and a selective supply unit that selectivelyswitches one of the plurality of gateway units and supplies only a TDMsignal acquired from the one gateway unit to the TDM network; whereineach of the plurality of gateway units includes at least one receivingbuffer, at least one jitter buffer, a unit that generates a read pointerfor the jitter buffer, a same packet supply unit that takes in a packetsupplied only from one of the packet networks, duplicates this packet togenerate a packet of a same content, and supplies it to another gatewayunit different from a local gateway unit, a receiving buffer controlunit that sequentially writes and reads both a packet taken in by thelocal gateway unit and a packet supplied from another gateway unitdifferent from the local gateway unit into and from the receivingbuffer, a valid packet supply unit that uses a packet read out firstfrom the receiving buffer as a valid packet and discards a packet of thesame content read out later in duplicate as an invalid packet, therebysupplying only the valid packet to the jitter buffer, and a jitterbuffer control unit that writes, for each packet supplied by the validpacket supply unit, the packet into the jitter buffer in accordance withthe common write pointer corresponding to the packet, and sequentiallyreads out a written packet from the jitter buffer in accordance with thejitter buffer read pointer and provides it for the TDM conversionprocessing.
 4. The redundancy gateway system according to claim 3,further comprising a processing timing signal generating unit thatgenerates a common processing timing signal with a predetermined cycle,wherein all the plurality of gateway units carry out writing and readingoperations to and from their own jitter buffers that they have,synchronously with the common processing timing signal.
 5. Theredundancy gateway system according to claim 4, wherein the processingtiming signal generating unit generates a common processing timingsignal with a cycle synchronized with the TDM signal as thepredetermined cycle.
 6. The redundancy gateway system according to claim3, wherein the common write pointer generating unit and the unit thatgenerates the read pointer are provided in each of the plurality ofgateway units, and only one gateway unit corresponding to an operationcommand generates the write pointer and the read pointer and commonlysupplies them to all the gateway units.
 7. The redundancy gateway systemaccording to claim 4, wherein the common write pointer generating unitand the unit that generates the read pointer are provided in each of theplurality of gateway units, and only one gateway unit corresponding toan operation command generates the write pointer and the read pointerand commonly supplies them to all the gateway units.
 8. The redundancygateway system according to claim 3, wherein each of the gateway unitsincludes a unit that generates a write pointer and a read pointer forthe receiving buffer for each of the packets, and only one gateway unitcorresponding to an operation command generates the write pointer andthe read pointer for the receiving buffer and commonly supplies them toall the gateway units, and the receiving buffer control units of all thegateway units control writing or reading of a packet to or from acontrol target receiving buffer in accordance with the write pointer andthe read pointer supplied thereto.
 9. The redundancy gateway systemaccording to claim 4, wherein each of the gateway units includes a unitthat generates a write pointer and a read pointer for the receivingbuffer for each of the packets, and only one gateway unit correspondingto an operation command generates the write pointer and the read pointerfor the receiving buffer and commonly supplies them to all the gatewayunits, and the receiving buffer control units of all the gateway unitscontrol writing or reading of a packet to or from a control targetreceiving buffer in accordance with the write pointer and the readpointer supplied thereto.